Saturday, October 29, 2011

NZ Post-Earthquake Demographics

5 days ago, Stats NZ released the first population data about a time after the Canterbury earthquakes in Feb 2011. Note that it is for June, just 4 months after the quake, and that things could have changed significantly between June and now. Here I make a few observations:

  • Only 10,600 people migrated out of Christchurch (net). This in only 2.9% or 1 in 35. (it is 12,200 compared to what would be expected without the earthquakes - 3.1% or 1 in 31)
  • It was mainly young people who left, 0-14 year olds decreased 7%, and 15-39 year olds decreased 3.8% in Christchurch City, older groups actually increased (whether by natural increase or inward migration).
  • Using the net migration trend over the previous 4 years as a base, out of the people who left Christchurch because of the earthquake, it looks like only 28% max settled elsewhere in the South Island. 29% max moved to the North Island, and 43% min moved overseas.
  • The natural increase and 'normal' migration to the South Island over a year was almost exactly canceled out by people leaving the South Island because of the earthquakes. The total population of the South Island in June 2011 was the same as a year before.
  • Since the people leaving shakey town were young, the median South Islander is now 3 1/2 years older than the median North Islander, compared to 3 years in June 2010. (the median North Islander normally ages 2 months/year, but earthquake migrants actually cancelled this out for a year)
Now for a couple of things not specifically related to the earthquake:
  • Out of 43 "Territorial Authorities" in the North Island, between 2006 and 2010, 30 grew in population, Horowhenua held steady, and 12 declined. This is basically a steady overall growth plus a gradual migration from the countryside to the cities.
  • Out of the 23 in the South Island, all of them grew except Gore. The overall growth is slightly higher, and the urban migration is more even, so it's not as noticeable.
  • In the North Island, when you take into consideration only the 0-14 year olds, only 9 Territorial Authorities grew, 1 held steady, and 33 declined. This shows a bit about the nature of the population growth.
  • In the North Island excluding Auckland, there is an overall growth in population and decline in 0-14 year olds.
In this image, the dark green areas are territorial authorities with declining populations (2006-2010), the light green have growing population but declining numbers of 0-14 year olds, gray areas have steady numbers of 0-14 year olds, orange has numbers of 0-14 year olds growing at less than 1% pa, and red areas have greater than 1% pa growth in 0-14 year olds.

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